The present invention relates to a method of assembling a bearing housing for rotary shafts of the type comprising a bearing cap secured to a relatively massive component, the bearing cap and the massive component affording respective semi-circular recesses which cooperate to define a circular hole in which a rotary shaft is received. An example of such a bearing housing is for an engine camshaft and in this case the massive component to which the bearing cap is connected, typically by two bolts, is a cylinder head. The rotary shaft engages the surface of the circular hole either directly or indirectly via a thin strip of e.g. softer metal with which the hole is lined, in each case with the interposition of a thin oil film.
It is of course essential for the smooth rotation of the shaft that the hole is precisely circular. It is in practice not possible for the bearing cap and the massive component to be manufactured with precisely semi-circular recesses and for the bearing housing then simply to be assembled around the shaft because the relative positions of the bolt holes and the semi-circular recesses can not be sufficiently accurately predetermined. If this technique is adopted the hole in practice always has a degree of non-circularity.
Accordingly, the bearing cap and the massive component are in practice manufactured with substantially semi-circular recesses and are then connected together, e.g. by bolts. The hole is then bored out in situ to ensure that it is truly circular. The bolts and the bearing cap are then removed and the shaft placed in position and the bearing cap then replaced. It is, however, essential that the bearing cap is aligned in precisely the same position as previously to ensure the necessary circularity of the hole.
Various alignment techniques are known for ensuring the precisely correct relocation of the bearing cap on the massive component and these include the use of dowels, locating bolts and lock notches and the use of very accurately machined and tight fitting bolts which do not permit any positional inaccuracy. The latter technique is the easiest and least costly but there is the risk that when the bolts are tightened the bearing cap will tilt and thus create an edge load on the shaft. This can result in higher bearing friction. The use of dowels, notches or the like can eliminate the problem of tilting but the dowel location holes on the bearing cap and the massive component must be machined separately and the pitch errors which can occur lead to difficulties in removing the bearing caps prior to installation of the shaft.
It is the object of the present invention to provide a method of assembling a bearing housing of the type referred to above which is both cheap and simple and does not suffer from the various disadvantages discussed above.
According to the present invention, a method of assembling a bearing housing for a rotary shaft of the type referred to above comprises connecting the bearing cap to the massive component, deforming at least two spaced portions of one of the bearing cap and the massive component into intimate contact with the other of the bearing cap and the massive component, boring the circular hole in the bearing cap and the massive component, removing the bearing cap, inserting the shaft into the semi-circular recess afforded by the massive component and reconnecting the bearing cap to the massive component.
In the method in accordance with the invention, spaced portions of the bearing cap are deformed into intimate contact with the massive or large component prior to boring the circular hole for accommodating the rotary shaft. This deformation defines a unique relocation position for the bearing cap with respect to the large component which means that when the bearing cap is again relocated on the large component it automatically adopts this unique position, that is to say the position in which the two precisely semi-circular recesses afforded by the bearing cap and the large component are precisely aligned with one another to define a truly circular hole in which the rotary shaft is accommodated. The bearing cap may thus be precisely repositioned without the use of dowels, locating bolts and the like, as referred to above. The intimately contacting surface regions of the bearing cap and the large component provide an increased surface area for receiving the clamping forces of the bolts and also resist the tendency of the bearing cap to twist when the bolts are tightened. As a result of the fact that the positional accuracy of the location of the bearing cap with respect to the large component is ensured by the intimately contacting surface regions, there is no particular need for precise positional accuracy of the bolt holes or close machining tolerances of the mating screw threads which means that the bolt holes in the bearing cap may simply be cast in rather than having to be drilled and the screw thread pitch tolerance may be relaxed, both of which result in a financial economy in the manufacturing process.
Whilst it is possible for the circular hole to be bored out in its entirety after the bearing cap has initially been connected to the large component, it is preferred that both the bearing cap and the large component afford substantially semicircular recesses before the bearing cap is initially connected to the large component for the first time. These two semi-circular recesses will inevitably not line up precisely to form a truly circular hole and they are in any event preferably initially made somewhat undersized. However, this means that only a relatively small amount of material need be removed when the final boring or machining of the circular hole is performed.
Whilst the bearing cap may have a relatively large number of spaced portions which are deformed into intimate contact with the large component, it is preferred that there are only two such portions in the form of projecting lugs. These lugs are preferably diametrically offset with respect to the circular hole to be formed.
Each of the projecting lugs may be deformed or bent about a single axis and it is found in practice that this adequately restrains relative movement of the bearing cap and the large component in all directions other than the direction in which the two components are moved away from one another and thus adequately defines a precise relocation position in which the bearing cap is replaced when reconnecting it to the large component. It is, however, preferred that the deformation of the projecting lugs is more complex and that the surface portions of the bearing cap and the large component in intimate contact with one another positively restrain relative movement of the bearing cap and large component in all directions other than the direction in which these two components are moved apart from one another.
In one embodiment of the invention, the surface of the large component which is engaged by the bearing cap is afforded by an upstanding formation, in which a semi-circular recess is formed, the outer side surfaces directed away from each other of which formation have a respective recess formed in them into which a respective lug on the bearing cap is deformed.
In an alternative embodiment, the surface of the large component which is engaged by the bearing cap has one or more spaced holes formed in it on each side of the semi-circular recess into which the portions of the lugs on the bearing cap are deformed.
Further features and details of the invention will be apparent from the following description of certain specific embodiments which is given by way of example with reference to the accompanying diagrammatic drawings.